I'm just a novice mechanic myself but I went ahead and did it. The port is located where everybody said it was, the right of the battery and then keep your head down and you'll be able to see it and it is still technically on the A/C line. Basically to avoid unhooking unnecessary wires I took the two top screws off the front black plate with an 8mm socket slid that same front plate ALL the way to the left (you may have to bring it left and then down a bit to stay put) to allow me to work the refrigerant hose to the low pressure port. It's totally optional if you still want to unhook that sensor at the top, but its pretty easy just press on the small tab and then pull straight outwards. Once finished I slid it back to the right, hooked the screws back up. Just make sure you don't lose them caps when your trying to screw it on back on

 

Yes, I found it. My 2001 Expedition has a very hard to find low side port. I've worked on MANY auto a/c's and THAT was frustrating.
It is on the suction accumulator (pass. side firewall), but you probably can't see it unless you remove the bracket in front of it. I could barely get my big hand thru (next to the valve cover) and un-screw the cap.
Thank you - your info helped me. The wife is happy, now.